1. Field of the Invention
The present invention relates to a method of purifying the exhaust gasses for a reciprocating type of an internal combustion engine and an system for implementing the method.
2. Description of Related Art
Typically, catalytic converters, conventionally employed in exhaust systems for automobile engines, have the purpose of controlling exhaust gas emissions through the chemical conversion of hydrocarbons (HC), carbon monoxide (CO) and nitrogen oxides (NOx) into non-polluting components, such as water, carbon dioxide, and nitrogen and purifying the exhaust gas.
Conventional three-way catalytic converters make use of precious metal catalysts, such as platinum, rhodium and palladium, incorporated into a silicon oxide carrier, and must operate above a specific activation temperature of, for example, 350.degree. C. in order to adequately convert exhaust gas emissions to the aforementioned non-polluting components. Because the temperature of exhaust gas, under normal engine operating conditions when the engine is in a warmed up condition, normally ranges from 700 to 900.degree. C. and the catalytic converter is kept at a temperature well above its activation temperature, the desired level of exhaust gas emission control can be adequately obtained.
The catalytic converter, however, gradually increases in temperature with the exhaust gas when the engine operates before being sufficiently warmed up, the result being that exhaust gas emission control is ineffective for approximately the first 60 seconds after an engine start. As a result, hydrocarbons (HC), carbon monoxide (CO) and nitrogen oxides (NOx) contained in the exhaust gas are released into the atmosphere during the cold start until the catalytic converter reaches the effective activation temperature. This demonstrates the necessity of a means to quickly raise the temperature of catalyst to the effective activation temperature within, for example, approximately the first 20 seconds of engine operation after a cold start.
Various means of dealing with this problem have been proposed. For example, Japanese Unexamined Patent Publication No. 4-66715 proposes a system or device of solving the problem through the installation of an electric catalyst heater in an exhaust duct upstream from the catalytic converter, or in the catalytic converter itself in close proximity to the inlet thereof, with the purpose of quickly raising the temperature of the exhaust gas so as to force the catalyst to reach the effective activation temperature while the engine is warming up. Otherwise, Japanese Unexamined Patent Publication No. 6-1672 proposes an afterburner device which is installed in an exhaust duct upstream from the catalytic converter, or in the catalytic converter itself in close proximity to the inlet thereof, with the purpose of quickly raising the temperature of the exhaust gas so as to force the catalyst to reach the effective activation temperature while the engine is warming up.
These exhaust gas purifying systems equipped with the electric catalyst heater or the afterburner device are disadvantageous because these heater and afterburner demand construction of additional components which make the exhaust gas purifying system larger and more complex, and because they pose problems in regard to their integration into the overall design of the vehicle. Moreover, not only the electric heater demands a large amount of electrical power which necessitates the use of a higher capacity battery and alternator than would normally be required in the vehicle, but also a control box would be required for the electric heater, along with heavy gauge wiring, both of which would pose additional problems in integrating the design into the vehicle.